The invention relates generally to the determination of the constituents of flowable particulate substances.
More particularly, the invention relates to the determination of the constituents of flowable particulate substances, especially of flowable particulate foodstuffs, using infrared radiation.
A variety of methods is employed to measure the concentration of a constituent of a flowable particulate substance. Examples are NMR, microwave and capacitive measuring methods. In practice, however, only a few of these methods are in widespread use, some for the measurement of a single constituent only.
It is known to measure the moisture of whole grain kernels by means of microwaves. Much more common in the grain processing industry, however, is the capacitive measurement of moisture content as described, for instance, in the present assignee's German Offenlegungsschrift 30 24 794. This method makes it possible to determine the moisture content of whole grain kernels, and to moistening to a predetermined moisture content, with a high degree of precision.
Capacitive measurement is carried out with a plate capacitor having a large area. The sample is advantageously conveyed past the capacitor plates which is ideal for an in-line measurement, that is, a measurement in the production line. By appropriate design of the measuring passage, average sample values can be obtained.
For the on-line measurement of the moisture content flour and semolina with NIR (near infrared radiation), the sample must be handled in an opposite manner. Thus, NIR measurement requires not only a light source but also an optical system so that NIR measurement is a form of point measurement. Each movement, whether by the optical system or by the sample, creates problems and can cause fuzziness in the representation of the surface condition of the sample.
These problems are effectively eliminated by subjecting the sample to predetermined conditions, e.g., as regards pressure and density, for the NIR measurement and, in addition, stopping the sample during the measurement as in the laboratory. The present assignee has been able to apply such a measuring procedure in practice with good results (European Patent Application 0 179 108). However, this procedure has the drawback that it is not possible to measure whole kernels, e.g., to determine the protein content of whole grain kernels. This leads to the following undesirable situation:
the moisture content of whole kernels is determined by a capacitive or, if necessary, microwave measuring technique, PA1 the protein content of flour is determined by the NIR measuring technique, and PA1 the protein content of whole kernels must be determined in the laboratory.
Furthermore, there are currently many special devices for on-line measurement of intermediate mill products, e.g., to determine product color. A calibration is carried out with a calibrating specimen in order to correct for all interfering parameters.
A great drawback of these devices stems from the fact that they require the use of three to five fundamentally different wavelength ranges, from gamma rays to microwaves, in a single production plant such as a mill. Thus, the measurement results can frequently be compared only with great difficulty although the product, which is initially in the form of whole kernels and later in the form of semolina or flour, remains basically the same.